U.S. patent number 4,799,177 [Application Number 06/815,038] was granted by the patent office on 1989-01-17 for ultrasonic instrumentation for examination of variable-thickness objects.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Dennis P. Sarr.
United States Patent |
4,799,177 |
Sarr |
January 17, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
Ultrasonic instrumentation for examination of variable-thickness
objects
Abstract
Ultrasonic apparatus and methods for detecting defects in a part
include a plurality of transducer channels, at least one of which
is dedicated to determining the thickness of the part. An initial
thickness value is determined and stored, and then subsequent
thickness estimates are compared to the original thickness value
and, if the estimates bear a predetermined relationship with the
stored thickness value, then the thickness estimates become the new
thickness values.
Inventors: |
Sarr; Dennis P. (Kent, WA) |
Assignee: |
The Boeing Company (Seattle,
WA)
|
Family
ID: |
25216690 |
Appl.
No.: |
06/815,038 |
Filed: |
December 31, 1985 |
Current U.S.
Class: |
702/171; 73/625;
73/628 |
Current CPC
Class: |
G01B
7/02 (20130101); G01N 29/11 (20130101); G01N
29/30 (20130101); G01N 29/34 (20130101); G01N
29/4427 (20130101); G01N 29/48 (20130101); G01N
2291/044 (20130101) |
Current International
Class: |
G01N
29/11 (20060101); G01N 29/34 (20060101); G01N
29/22 (20060101); G01N 29/30 (20060101); G01N
29/04 (20060101); G01B 7/02 (20060101); G01N
29/48 (20060101); G01N 29/44 (20060101); G01N
029/00 () |
Field of
Search: |
;364/503,506,507,552,570
;73/610,611,612,622,624,625,628,636,644,598 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
0063560 |
|
Apr 1984 |
|
JP |
|
2093185 |
|
Aug 1982 |
|
GB |
|
Primary Examiner: Lall; Parshotam S.
Assistant Examiner: Trans; V. N.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner
Claims
What is claimed is:
1. An apparatus for ultrasonic inspection of a part comprising:
means for generating a transmission signal;
a plurality of transducer channels, coupled to said transmission
signal generating means, for generating ultrasonic pulses for
transmission into said part, for receiving portions of said
ultrasonic pulses from said part, and for creating electrical
reflection signals representing said portions, one of said
transducer channels being a thickness transducer channel and
including means for determining a part thickness value representing
the thickness of a portion of said part adjacent said thickness
transducer channel;
means, coupled to each of said transducer channels, for measuring
the amplitude of said electrical reflection signals only during a
time window corresponding to said part thickness value; and
thickness gating means, coupled to said measuring means, for
automatically replacing said part thickness value with a
subsequently determined part thickness value, and thereby adjusting
said time window, according to electrical reflection signals
received by said thickness transducer channel only if said
subsequently determined part thickness value differs from said part
thickness value by less than a predetermined difference value.
2. The apparatus of claim 1 wherein said thickness gating means
includes:
adjustable means for presetting said part thickness value;
means for evaluating said electrical reflection signals received by
said thickness transducer channel to determine a part thickness
estimate; and
means for replacing said part thickness value with said part
thickness estimate when said part thickness value and said part
thickness estimate bear a predetermined relationship with each
other.
3. The apparatus of claim 2 further including
a visual display device coupled to at least one of said transducer
channels for displaying said electrical reflection signals; and
means, coupled to said display device, for generating a blanking
signal having a duration related to the onset of said transmission
signal and the receipt of said first major signal portion for
blanking out from said display a corresponding portion of said
displayed electrical reflection signals.
4. The apparatus of claim 2 wherein portions of said electrical
reflection signals having amplitudes greater than a predetermined
threshold are termed major reflection portions and wherein said
evaluating means includes
means for selecting from said thickness transducer channel's
electrical reflection signals a first major signal portion
representing the front surface of said part;
means for selecting from said thickness transducer channel's
electrical reflection signals a second major signal portion,
received after said first signal portion; and
means for forming said part thickness estimate from the time
difference between receipt of said first major signal portion and
said second major signal portion.
5. The apparatus of claim 4 wherein said replacing means
includes:
means for storing said part thickness value;
means for generating a representation of said part thickness
estimate;
means for comparing said said part thickness estimate
representation and said stored part thickness value and for
generating a comparison signal if said part thickness value and
said part thickness estimate bear said predetermined relationship
with each other; and
mens, responsive to said comparison signal, for storing said part
thickness estimate in said storing means, thereby replacing said
part thickness value with said part thickness estimate.
6. The apparatus of claim 5 wherein said comparing means includes a
amplifier circuit to multiply said part thickness estimate by
values corresponding to said predetermined relationship.
7. The apparatus of claim 5 wherein said thickness gating means
also includes
means for generating a ramp signal related to the time elapsed from
the onset of said transmission signal; and
means for comparing said ramp signal to said part thickness value
to generate a sample pulse representing said time window.
8. The apparatus of claim 7 wherein said measuring means includes a
peak detector circuit coupled to said comparing means for
determining the peak value of said electrical reference signals
received by said transducer channels.
9. The apparatus of claim 8 wherein said measuring means also
includes a computer.
10. The apparatus of claim 1 further including
a visual display device coupled to at least one of said transducer
channels for displaying said electrical reflection signals; and
means, coupled to said display device, for generating a blanking
signal to blank out a portion of said displayed electrical
reflection signals.
11. The apparatus of claim 1 wherein said measuring means includes
a logarithmic amplifier for adjusting the dynamic range of said
electrical reflection signals.
12. A method of nondestructive ultrasonic testing of a part
comprising the steps of:
generating a transmission signal;
transmitting ultrasonic pulses into said part using a plurality of
transducer channels;
receiving and transducing portions of said ultrasonic pulses and
creating electrical reflection signals representing those
portions;
determining, from one of said transducer channels being termed a
thickness transducer channel, a part thickness value representing
the thickness of a portion of said part adjacent said thickness
transducer channel;
measuring the amplitude of said electrical reflection signals only
during a time window corresponding to said part thickness value;
and
automatically replacing said part thickness value with a
subsequently determined part thickness value, and thereby adjusting
said time window, according to electrical reflection signals
received by said thickness transducer channel only if said
subsequently determined part thickness value differs from said part
thickness value by less than a predetermined difference value.
13. The method in claim 12 wherein said step of automatic adjusting
includes the steps of:
presetting said part thickness value;
evaluating said electrical reflection signals received by said
thickness transducer channel to determine a part thickness
estimate; and
replacing said part thickness value with said part thickness
estimate when said part thickness value and said part thickness
estimate bear a predetermined relationship with each other.
14. The method of claim 13 wherein portions of said electrical
signals having amplitudes greater than a predetermined threshold
are termed major reflection portions, and
wherein said evaluating step includes the steps of:
selecting from said thickness transducer channel's electrical
reflection signals a first major signal portion representing the
front surface of said part;
selecting from said thickness transducer channel's electrical
reflection signals a second major signal portion received after
said first signal portion; and
forming said part thickness estimate from the time difference
between receipt of said first major signal portion and said second
major signal portion.
15. The method of claim 14 wherein said replacing step includes the
steps of:
storing said part thickness value;
generating a representation of said part thickness estimate;
comparing said representation of said part thickness estimate and
said part thickness value;
generating a comparison signal if said part thickness value and
said part thickness estimate representation bear said predetermined
relationship with each other; and
storing said part thickness estimate in said storing means in
response to said comparison signal, thereby replacing said part
thickness value with said part thickness estimate.
16. The method of claim 15 wherein said automatic adjusting step
includes the steps of:
generating an analog ramp signal related to the time elapsed from
the onset of said transmission signal; and
comparing said analog ramp signal to said part thickness value to
generate a sample pulse representing said time window.
17. The method of claim 16 wherein said measuring step includes the
step of determining the peak value of said electrical reference
signals received by said transducer channels during said sample
pulse duration; and
wherein said comparing step includes the step of generating said
sample pulse with a predetermined time duration.
18. The method of claim 17 further including the steps of
displaying said electrical reflection signals for at least one
transducer channel; and
generating a blanking signal to prevent displaying unwanted
portions of said displayed electrical reflection signals, and
wherein said replacing step includes the steps of:
storing said part thickness value;
generating an analog voltage level representing said part thickness
estimate;
comparing said analog voltage level representing said part
thickness estimate and said part thickness value;
generating a comparison signal if said part thickness value and
said part thickness estimate analog voltage levels bear said
predetermined relationship with each other; and
storing said part thickness estimate in said storing means in
response to said comparison signal, thereby replacing said part
thickness value with said part thickness estimate.
19. An apparatus for ultrasonic inspection of a part
comprising:
means for generating a transmission signal;
a plurality of transducer channels, coupled to said transmission
signal generating means, for generating ultrasonic pulses for
transmission into said part, for receiving ultrasonic pulses from
said part, and for creating electrical reflection signals
representing said pulses, those portions of said electrical
reflection signals having amplitudes greater than a predetermined
threshold being termed major reflection portions, one of said
transducer channels being a thickness transducer channel and
including means for determining a value representing the thickness
of a portion of said part adjacent said thickness transducer
channel;
thickness gating means for automatically adjusting said part
thickness value, and thereby a time window, according to electrical
reflection signals received by said thickness transducer channel,
said thickness gating means including:
adjustable means for presetting said part thickness value;
means for evaluating said electrical reflection signals received by
said thickness transducer channel to determine a part thickness
estimate, said evaluating means including means for selecting from
said thickness transducer channel's electrical reflection signals a
first major signal portion representing the front surface of said
part;
means for selecting from said thickness transducer channel's
electrical reflection signals a second major signal portion,
received after said first signal portion; and
means for forming said part thickness estimate from the time
difference between receipt of said first major signal portion and
said second major signal portion;
means for replacing said part thickness value with said part
thickness estimate when said part thickness value and said part
thickness estimate bear a predetermined relationship with each
other, said replacing means including
means for storing said part thickness value;
means for generating a representation of said part thickness
estimate;
means for comparing said said part thickness estimate
representation and said stored part thickness value and for
generating a comparison signal if said part thickness value and
said part thickness estimate bear said predetermined relationship
with each other; and
means, responsive to said comparison signal, for storing said part
thickness estimate in said storing means, thereby replacing said
part thickness value with said part thickness estimate;
means for generating a ramp signal related to the time elapsed from
the onset of said transmission signal; and
means for comparing said ramp signal to said part thickness value
to generate a sample pulse representing said time window, said ramp
signal comparing means including a monostable multivibrator for
generating said sample pulse with a predetermined time duration;
and
means, coupled to each of said transducer channels and to said
thickness gating means, for measuring the amplitude of said
electrical reflection signals only during a time window
corresponding to said part thickness value, said measuring means
including a peak detector circuit coupled to said comparing means
for determining the peak value of said electrical reference signals
received by said transducer channels and including means for being
activated only during said predetermined time duration.
20. An apparatus for ultrasonic inspection of a part
comprising:
means for generating a transmission signal;
a plurality of transducer channels, coupled to said transmission
signal generating means, for generating ultrasonic pulses for
transmission into said part, for receiving said ultrasonic pulses
from said part, and for creating electrical reflection signals
representing said pulses, portions of said electrical reflection
signals having amplitudes greater than a predetermined threshold
being termed major reflection portions, one of said transducer
channels being a thickness transducer channel and including means
for determining a value representing the thickness of a portion of
said part adjacent said thickness transducer channel;
thickness gating means for automatically adjusting said part
thickness value, and thereby a time window, according to electrical
reflection signals received by said thickness transducer channel,
said thickness gating means including
adjustable means for presetting said part thickness value;
means for evaluating said electrical reflection signals received by
said thickness transducer channel to determine a part thickness
estimate, said evaluating means including means for selecting from
said thickness transducer channel's electrical reflection signals a
first major signal portion representing the front surface of said
part;
means for selecting from said thickness transducer channel's
electrical reflection signals a second major signal portion,
received after said first signal portion; and
means for forming said part thickness estimate from the time
difference between receipt of said first major signal portion and
said second major signal portion;
means for replacing said part thickness value with said part
thickness estimate when said part thickness value and said part
thickness estimate bear a predetermined relationship with each
other, and
means for generating a sample gate signal from said part thickness
value, said sample pulse occurring at an estimated time of receipt
by said transducer channels of reflections from a rear surface of
said part; and
means, coupled to each of said transducer channels and to said
thickness gating means, for measuring the amplitude of said
electrical reflection signals only during a time window
corresponding to said part thickness value, said measuring means
being activated only during said sample gate signal.
21. The apparatus of claim 20 wherein said plurality of transducer
channels each includes two ultrasonic transducers positioned on
opposite sides of said part.
22. The apparatus of claim 20 wherein said plurality of transducer
channels each includes a single ultrasonic transducer element for
generating and receiving said ultrasonic pulses.
23. An apparatus for ultrasonic inspection of a part
comprising:
means for generating a transmission signal;
a plurality of transducer channels, coupled to said transmission
signal generating means, for generating ultrasonic pulses for
transmission into said part, for receiving said ultrasonic pulses
from said part, and for creating electrical reflection signals
representing said pulses, portions of said electrical reflection
signals having amplitudes greater than a predetermined threshold
being termed major reflection portions, one of said transducer
channels being a thickness transducer channel and including means
for determining a value representing the thickness of a portion of
said part adjacent said thickness transducer channel;
thickness gating means for automatically adjusting said part
thickness, and thereby a time window, according to electrical
reflection signals received by said thickness transducer channel,
said thickness gating means including
adjustable means for presetting said part thickness value;
means for evaluating said electrical reflection signals received by
said thickness transducer channel to determine a part thickness
estimate, said evaluating means including
means for selecting from said thickness transducer channel's
electrical reflection signals a first major signal portion
representing the front surface of said part;
means for selecting from said thickness transducer channel's
electrical reflection signals a second major signal portion,
received after said first signal portion; and
means for forming said part thickness estimate from the time
difference between receipt of said first major signal portion and
said second major signal portion;
means for replacing said part thickness value with said part
thickness estimate when said part thickness value and said part
thickness estimate bear a predetermined relationship with each
other;
means for generating a sample gate signal from said part thickness
value, said sample pulse occurring approximately at the time of
receipt by said transducer channels of reflections from the
interior portion of said part between a rear surface of said part
and said front surface of said part; and
means, coupled to each of said transducer channels and to said
thickness gating means, for measuring the amplitude of said
electrical reflection signals only during a time window
corresponding to said part thickness value, said measuring means
being activated only during said sample gate signal.
24. The apparatus of claim 23 wherein said plurality of transducer
channels each includes two ultrasonic transducers positioned on
opposite sides of said part.
25. The apparatus of claim 23 wherein said plurality of transducer
channels ech includes a single ultrasonic transducer element for
generating and receiving said ultrasonic pulses.
26. An apparatus for ultrasonic inspection of a part
comprising:
means for generating a transmission signal;
a plurality of transducer channels, coupled to said transmission
signal generating means, for generating ultrasonic pulses for
transmission into said part, for receiving ultrasonic pulses from
said part, and for creating electrical reflection signals
representing said pulses, those portions of said electrical
reflection signals having amplitudes greater than a predetermined
threshold being termed major reflection portions, one of said
transducer channels being a thickness transducer channel and
including means for determining a value representing the thickness
of a portion of said part adjacent said thickness transducer
channel; thickness gating means, coupled to said measuring means,
for automatically adjusting said part thickness value, and thereby
a time window, according to electrical reflection signals received
by said thickness transducer channel, said thickness gating means
including:
adjustable means for presetting said part thickness value;
means for evaluating said electrical reflection signals received by
said thickness transducer channel to determine a part thickness
estimate, said evaluating means including
means for selecting froms aid thickness transducer channel's
electrical reflection signals a first major signal portion
representing the front surface of said part;
means for selecting from said thickness transducer channel's
electrical reflection signals a second major signal portion,
received after said first signal portion; and
means for forming said part thickness estimate from the time
difference between receipt of said first major signal portion and
said second major signal portion;
means for replacing said part thickness value with said part
thickness estimate when said part thickness value and said part
thickness estimate bear a predetermined relationship with each
other, said replacing means including
means for storing said part thickness value;
means for generating a representation of said part thickness
estimate;
means for comparing said said part thickness estimate
representation and said stored part thickness value and for
generating a comparison signal if said part thickness value and
said part thickness estimate bear said predetermined relationship
with each other; and
means, responsive to said comparison signal, for storing said part
thickness estimate in said storing means, thereby replacing said
part thickness value with said part thickness estimate;
means for generating a ramp signal related to the time elapsed from
the onset of said transmission signal;
means for comparing said ramp signal to said part thickness value
to generate a sample pulse representing said time window; and
means, coupled to each of said transducer channels and to said
thickness gating means, for measuring the amplitude of said
electrical reflection signals only during a time window
corresponding to said part thickness value, said measuring means
including a peak detector circuit coupled to said comparing means
for determining the peak value of said electrical reference signals
received by said transducer channels, said peak detector circuit
including:
a capacitor coupled to one of said electrical reflection
circuits;
a transistor, coupled to said capacitor for resetting said
capacitor; and
a sample and hold circuit coupled to said capacitor and controlled
by said sample pulse.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The invention is related to the following copending U.S. patent
applications assigned to the assignee of the present invention:
DATA RECORDING APPARATUS FOR AN ULTRASONIC INSPECTION SYSTEM, Ser.
No. 06/815,050, filed on Dec. 31, 1985 by D. P. Sarr;
ULTRASONIC INSPECTION SYSTEM WITH LINEAR TRANSDUCER ARRAY, Ser. No.
06/815,047, filed on Dec. 31, 1985 by D. P. Sarr and F. D.
Young;
ULTRASONIC INSPECTION SYSTEM APPARATUS AND METHOD, Ser. No.
06/815,048, filed on Dec. 31, 1985 by D. P. Sarr;
AN IMPROVED ULTRASONIC TESTING APPARATUS, Ser. No. 06/815,163,
filed Dec. 31, 1985 by G. A. Geithman and D. P. Sarr;
ULTRASONIC TRANSDUCER WITH SHAPED BEAM INTENSITY PROFILE, Ser. No.
06/815,162, filed Dec. 31, 1985 by G. A. Geithman and D. H.
Gilbert, now U.S. Pat. No. 4,700,575; and
ULTRASONIC 64 CHANNEL INSPECTION SYSTEM WITH MULTIGATE/MULTI MODE
SELECTION SOFTWARE CONFIGURABILITY, Ser. No. 06/815,044, filed Dec.
31, 1985 by D. P. Sarr.
BACKGROUND OF THE INVENTION
The present invention relates to the field of ultrasonic defect
detecting systems, and especially to such systems which are used
for nondestructive inspection (NDI) of elements having varying
thicknesses. This invention has particular application in the
testing of aircraft structures made from graphite/epoxy
materials.
There are three major types of NDI systems which are used for
testing elements, for example, aircraft parts: loss-of-back (LOB),
pulse echo (PE) and through transmission ultrasonic (TTU). The LOB
technique compares a predetermined threshold value with the peak
amplitude of the ultrasonic reflections from an element's rear
surface, i.e., the surface most distant from the ultrasonic
transducers. If the element has no defects in the volume between
the front and back surfaces proximate the transducers, then the
peak amplitude of the reflections from the back surface should
exceed the threshold. If a defect is present in that volume, the
peak amplitude of the signal reflected by the rear surface
decreases significantly, in fact below the threshold, because the
defect reflects much of the ultrasonic energy before it ever
reaches the rear surface.
FIGS. 1A and 1B, which show voltage signals corresponding to
ultrasonic reflections from an element having no defects and having
a defect, respectively, illustrate this phenomenon. There are three
major reflection portions in FIG. 1A. The portion that occurs
first, which is the leftmost in FIG. 1A, is an artifact from the
ultrasonic pulse transmitted toward the element (sometimes called
the "Main Bang"). The next major portion is a reflection from the
front surface of the element. The third major portion (the
rightmost) is a reflection from the rear surface. Since FIG. 1A
corresponds to the reflections received from an element with no
defects, the peak amplitude of the reflections from the rear
surface is above the predetermined threshold V.sub.N, thereby
indicating the absence of any defects.
In FIG. 1B, there are four major signal portions proceeding in
order from left to right corresponding in time to their receipt by
an ultrasonic transducer. The first, and largest, is the artifact
from the Main Bang, the second represents a reflection from the
front surface of a part, the third represents a reflection from a
defect in the interior of the part, and the fourth represents a
reflection from the rear surface of the part. Because the defect
reflects some of the ultrasonic energy that penetrates the front
surface, a smaller amount of energy is available to be reflected
from the rear surface. As FIG. 1B shows, that rear surface
reflection is below the predetermined threshold V.sub.N, so the
presence of a defect is noted.
FIGS. 1A and 1B also show the concept of a time window which is
used for finding the proper signals for testing. The time period
denoted T.sub.R indicates a time window during which reflections or
transmitted signals from the rear surface are expected to be
received. It is important in the LOB technique to know when that
window should begin and end to ensure that the reflections being
examined are those from the rear surface, and not those from a
defect or the front surface.
The PE technique bears some similarity to the LOB technique.
However, instead of examining the peak amplitude of the rear
surface reflection as the LOB technique requires, the PE techniques
tests the peak amplitudes of the reflections from the element's
interior, i.e., from between the front and rear surfaces. If any
reflections from the interior above a certain threshold level are
received, those reflections are evidence of a defect. If no
sufficiently large reflections are received from the element
interior, then the element portion under investigation is deemed
defect-free.
The TTU technique differs from the above techniques in that it
requires two transducers for each transducer channel, the
transducers being located on opposite sides of the element to be
examined. Instead of examining ultrasonic reflections, however, the
TTU technique involves determining the amount of ultrasonic energy
that was able to pass entirely through the part.
As the above methods indicate, it is extremely important to control
the time window in which the examination takes place. For example,
in the LOB method, the time window must be such as to capture only
reflections from the rear surface (see T.sub.R in FIGS. 1A and 1B).
In the PE method, it is extremely important to obtain a time window
that captures reflections between the front and rear surfaces, and
which does not include reflections from either of those surfaces
(see time window T.sub.I in FIGS. 1A and 1B).
It is not difficult to identify the reflection from the front
surface because that is the first reflection that occurs after the
Main Bang artifact. If the element being examined has a varying
thickness, however, it becomes very difficult to determine where
the rear surface is because the location of that surface changes in
relation to the front surface, and hence the corresponding time
windows related to the rear surface must also change. Furthermore,
the only ultrasonic information which is available to find the rear
surface are the reflections from the part under test. However, as
FIGS. 1A and 1B show, the reflections from a defect and from a rear
surface appear very similar. Furthermore, by the time a reflection
is properly identified, the ultrasonic detector is usually making
another measurement.
One solution to this problem has been to determine thickness
mechanically with a calibrated roller, for example. Rollers,
however, react slowly and are inaccurate not only because they may
lose contact with the surface, but also because the rollers
experience wear which gradually makes their measurements imprecise.
In addition, rollers cannot be used in many instances. For example,
an element may be mounted or configured in a manner to preclude the
use of a roller, or the temperature of the elements, for example
molten steel sheets, may be too extreme for rollers.
Another way of solving the problem was discussed in U.S. Pat. No.
3,942,358 to Pies. The device in this patent includes an array of
transducers which both transmit and receive ultrasonic pulses in
the PE mode. The transducers are coupled to electric circuitry
which measures the time difference between receipt of the surface
reflection and the next major reflection, and then finds the
maximum time difference. That maximum time difference is stored and
compared to the maximum speed elapsed times determined from
succeeding scans. Whenever a maximum time measurement from a
succeeding scan exceeds the stored amount, the new maximum time is
stored in place of the old value. The result of the entire
operation is that the maximum time difference for the entire
element, and hence the maximum thickness, is stored and used to set
a time window corresponding to the rear surface.
In this system, however, two ultrasonic scans need to be made for
each element. The first scan determines the maximum thickness, and
the second scan then looks for defects. In addition, since each
transducer channel is used for determining thickness during one
scan and defects during the next scan, the electronics of this
system can become rather complex.
Pies does recognize that for elements of varying thickness, the
transmit times could be updated during the scans. This still
results in complicated circuitry, however, to perform the thickness
measurement task. The system in Pies also cannot detect extensive
defects.
It is therefore an object of this invention to provide fast and
accurate NDI ultrasonic testing of parts.
Another object of this invention is accurate NDI testing without
the use of complicated circuitry.
SUMMARY OF THE INVENTION
The present invention overcomes the problems of the prior art and
achieves the objects of this invention with NDI testing apparatus
and methods employing a plurality of transducer channels for
examining the signals reflected from or transmitted through a part
under test. At least one of those channels is dedicated to making
thickness measurements by examining reflections from the front and
rear surfaces. If the dedicated thickness channel(s) makes a
thickness measurement which differs from a current thickness value
by less than some predetermined amount, then that new measurement
replaces the old thickness value, since it is assumed that the new
measurement reflects a thickness change which is relatively slow.
If the thickness channel measurement differs from the current
thickness value by greater than the predetermined amount, then it
is assumed that the second reflection received was not from the
rear surface, but rather from a defect in the interior of the
element, and the current thickness value remains unchanged.
To achieve the objects and in accordance with the purposes of this
invention, as embodied and as broadly described herein, the
apparatus of this invention for ultrasonic inspection of a part
comprises means for generating a transmission signal; a plurality
of transducer channels, coupled to the transmission signal
generating means, for generating ultrasonic pulses for transmission
into said part, for receiving portions of said ultrasonic pulses,
and for creating electrical reflection signals representing said
portions, one of the transducer channels being a thickness
transducer channel and including means for determining a value
representing the thickness of a portion of the part adjacent to the
thickness transducer channel; means, coupled to each of the
transducer channels, for measuring the amplitude of the electrical
reflection signals only during a time window corresponding to the
part thickness value; and thickness gating means, coupled to the
measuring means, for automatically adjusting the thickness value,
and thereby the time window, according to the electrical reflection
signals received by the thickness transducer channel.
A method of ultrasonic inspection of a part according to this
invention comprises the steps of generating a transmission signal;
transmitting ultrasonic pulses into the part using a plurality of
transducer channels; receiving and transducing portions of that
transmitted ultrasonic pulse and creating electrical reflection
signals representing those portions; measuring the amplitude of the
electrical reflection channels only during a time window
corresponding to a part thickness value; and determining a part
thickness value by examining the electrical reflection signals from
one channel of the apparatus.
The accompanying drawings, which are incorporated in and which
constitute a part of the specification, illustrate one embodiment
of the invention and, together with the description, explain the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are representations of voltages corresponding to
ultrasonic reflections received from a part under inspection;
FIGS. 2 and 2A are a block diagram and a detailed circuit diagram,
respectively, of a System Pulse Controller of an embodiment of the
present invention;
FIGS. 3 and 3A are a block diagram and a detailed circuit diagram,
respectively, of a Transducer Array Electronics unit of the
embodiment of the present invention;
FIGS. 4 and 4A are a block diagram and a detailed circuit diagram,
respectively, of a Three-position Gate of the embodiment of the
present invention;
FIGS. 5 and 5A are a block diagram and a detailed circuit diagram,
respectively, of a Thickness Gate Controller of the present
invention;
FIGS. 6 and 6A are a block diagram and a detailed circuit diagram,
respectively, of a Log Amplifier and Peak Detector circuit of the
embodiment of the present invention;
FIG. 7 is a system diagram of the present invention;
FIG. 8 is a flow chart for an initialization routine of the
embodiment of the present invention; and
FIG. 9 is a timing diagram for explanation of the operation of the
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is now made in detail to a presently preferred embodiment
of the invention, an example of which is illustrated in the
accompanying drawings. The embodiment shown relates to an LOB
apparatus. Pesrons of ordinary skill in the art will recognize the
applicability of the invention to the PE and TTU systems for
nondestructive inspection.
FIGS. 2-7 relate to a preferred embodiment of the ultrasonic
testing apparatus of the present invention. FIG. 7 is a system
diagram which shows system elements and their interrelationship,
and FIGS. 2-6 show each element of the system in detail. The block
elements in each of the block diagrams (FIGS. 2-6) correspond to
the simiarly numbered components shown by the dotted lines around
certain circuit elements in the corresponding circuit diagrams
(FIGS. 2A-6A).
FIGS. 2-7 show that there are five major components of the system.
The System Pulse Controller (FIGS. 2 and 2A) generates the initial
timing for the system and there is one of these components per
system. In response to controls set on a panel, the System Pulse
Controller generates an MB (Main Bang) Clock and PULSER COMMAND
(hereafter referred to without the inverting bar) signals. The MB
Clock signal period is the same as the time between transmissions
of ultrasonic pulses into the element or part under test. The
PULSER COMMAND signals each correspond to a different transducer
channel and are used both to activate the transmitted ultrasonic
pulse for that channel, and to synchronize the operation of the
channel electronics with remainder of the system.
The second major system component is the Transducer Array
Electronics (FIGS. 3 and 3A) which provides the electrical
interfacing of the system with the transducer. In the present
embodiment, there is one of these components as shown in FIGS. 3
and 3A for each channel used. The Transducer Array Electronics
responds to the corresponding PULSER COMMAND signal to generate a
high voltage pulse that drives an ultrasonic transducer to transmit
an ultrasonic pulse toward the part or element. The electronics
also receives the transduced ultrasonic reflections (or
transmissions in the TTU mode) of that pulse and creates the
Ultrasonic Input Signal which is then analyzed for defect
testing.
The third major system component is the Three-position Gate (FIGS.
4 and 4A) which generates timing signals for a corresponding
transducer channel. Each of these Gates corresponds to a different
transducer channel. The Three-position Gate receives the PULSER
COMMAND and Ultrasonic Input Signal corresponding to the same
transducer channel. The Gates for all the transducer channels
generate a Blanking signal (shown in its inverted form in the
figures) which is used primarily for eliminating unwanted signals
from the corresponding oscilloscope trace, and for ensuring that
the peak detection circuitry, described below, tests the correct
portion of the Ultrasonic Input Signal. The Three-position Gate
also receives two other signals: a 15 MHz System clock and an Old
Part Thickness Analog signal. The second of those signals is an
analog voltage whose level corresponds to the determined part
thickness. From the System clock and the Old Part Thickness Analog
signal, the Three-position Gate generates two signals which are the
inverse of each other. The GATE signal is used for the oscilloscope
display and the SAMPLE signal is used to control the time window
during which the Ultrasonic Input is measured. The Three-position
Gate corresponding to the thickness transducer signal also
generates the System Material Enable signal, which is a pulse whose
duration corresponds with the current estimate for the thickness of
the part under investigation.
The fourth system component, called the Thickness Gate Controller
(FIGS. 5A and 5B), generates the 15 MHz System Clock and the Old
Part Thickness Analog signal used by the Three-position Gates.
There is only one Thickness Controller in the preferred embodiment.
This element compares the current Old Part Thickness Analog signal
with voltages representing new thickness estimates which are
derived from the System Material Enable signal. If the new estimate
differs from the Old Part Thickness Analog signal by less than a
predetermined amount, for example, 5%, the Thickness Controller
updates the Old Part Thickness Analog voltage signal by replacing
that signal with the new estimate.
The fifth component is called the Log Amplifier and Peak Detection
circuit (FIGS. 6A and 6B), and there is one of these for each
channel. This element processes the Ultrasonic Input signal for
display on a visual display device, such as an oscilloscope, and
also for detection of defects. The Log Amplifier and Peak Detection
circuit also examines the peaks of that signal within a time window
depending upon the SAMPLE pulse. The measured peaks during the time
window are then sent to a microcomputer in a preferred embodiment
for further evaluation.
With this overall system viewpoint, the specific operations of each
one of these elements will be easier to understand. The detailed
circuit diagrams for each element are shown, but not described in
detail because persons of ordinary skill in the art will, from the
diagrams, know the details of such circuit operation. In addition,
the system shown has eleven (11) transducer channels, but it should
be understood that either a fewer or a greater number of transducer
channels could also be used consistent with the present
invention.
In accordance with the present invention, the apparatus for
ultrasonic inspection of a part of this invention includes means
for generating a transmission signal. In the preferred embodiment
of the invention shown in the figures, the System Pulse Controller
shown in FIGS. 2 and 2A includes circuitry for generating a main
transmission signal, called the MB clock, and transmission signals
for each channel, called PULSER COMMAND signals. Repetition rate
controller 100 determines the rate of the MB Clock signal, which is
the rate at which ultrasonic transmission pulses are generated. In
FIG. 2A, which is the detailed circuit representation of the system
pulse control in FIG. 2, IC1 outputs a pulse at a rate which
depends upon the value of potentiometer VR1. Potentiometer VR1 is
panel-mounted and set by the operator of the system.
Coupled to the output of the repetition rate controller 100 is
pulse width generation and width control circuitry 110 which
controls the duration of the transmission pulses. The duration of
the transmission pulses is related to the amount of ultrasonic
energy that is transmitted into the part. FIG. 2A shows that the
specific circuitry for control circuitry 110 includes two
"one-shots" (also called monostable multivibrators) IC4 and IC5.
When triggered by the output of IC1, IC4 generates a one
microsecond pulse which is used to trigger IC5. IC5 generates two
pulses having opposite polarities. The duration of those pulses is
between 50 nanoseconds and 1.7 microseconds. The specific width of
the pulse depends upon the setting of potentiometer VR2. The
positive-going one of the two pulses is the MB Clock signal.
The remaining two elements shown in the System Pulser Controller of
FIGS. 2 and 2A are four bit counter 120 and channel select
circuitry 130. Counter 120 receives the output of the repetition
rate controller and generates a four-bit binary count that repeats
cyclically. Channel select circuitry 130 includes a demultiplexer
IC3 which receives the count output from IC2 and sequentially
generates single pulses, in order, from each of the output. Each of
those pulses serves as one input to a different NOR gate 135 in
circuitry 130, each such NOR gate 135 corresponding to one of the
channels. The other input to each of gates 135 is the inverse of
the MB Clock signal. The output of each NOR gate 135 is a PULSER
COMMAND signal for a different one of the transducer channels. The
PULSER COMMAND signal is a pulse with a width equal to that of the
MB Clock signal.
Corresponding to each transducer channel is a Transducer Array
Electronics system as shown in FIGS. 3 and 3A. The systems are used
to generate a high voltage signal to drive an ultrasonic transducer
in response to the corresponding PULSER COMMAND signal, and also to
generate an Ultrasonic Input signal from the reflections received
by the transducer.
The transmission electronics includes TTL buffer 200 to isolate the
PULSER COMMAND signal from the remainder of the circuitry, and a
MOS/FET Driver 210 to interface the PULSER COMMAND signal with a
MOS/FET High Voltage Transistor Switch 220. Transistor Switch 220
generates a high voltage pulse to drive the ultrasonic transducer
with a pulse whose duration is equal to the duration of the PULSER
COMMAND signal.
Ultrasonic receive electronics 230 are coupled to the output of the
transducer and change the voltage signals from that transducer into
signals of the proper level for further signal processing. If this
invention is used in the LOB or PE mode, then only one transducer
per channel is used, and the jumper, denoted by the dotted line, is
put in place to couple that transducer to the ultrasonic receiver
electronics 230. If the system is in the TTU mode, then the jumper
is not used, but instead the receiver input comes from the second
transducer, located on the opposite side of the part from the
transmission transducer, and which is connected to amplifier 230
via the dotted line.
Once the ultrasonic signals have been received and properly
amplified, then they must be examined to sense the presence of
defects. Accordingly, the present invention includes means for
measuring the amplitude of the electrical reflection signals from
the transducer channels only during a determined time window. That
time window corresponds to a part thickness value that represents
the thickness of the part at a portion adjacent to the thickness
channel transducer. In the preferred embodiment, the Log Amplifier
and Peak Detection circuitry shown in FIGS. 6 and 6A provide for
the measurement of the peaks of the corresponding Ultrasonic Input
Signal during a time window determined from the Blanking and SAMPLE
signals.
In the system and circuitry shown in FIGS. 6 and 6A, Peak Detector
540 receives the corresponding Ultrasonic Input signal from
amplifier 230 shown in FIGS. 3 and 3A. The Ultrasonic Input signal
is conditioned by a 50 ohm termination analog buffer 500, a log
amplifier 510, and an analog buffer 530 before being analyzed by
peak detector 540. The purpose of log amplifier 510 is to compress
the Ultrasonic Input signal into a signal range of 0-10 volts.
Typically, log amplifier 510 provides an 80 dB dynamic range, but
persons of ordinary skill in the art will recognize that the
dynamic range of such an amplifier is adjustable. The output of log
amplifier 510 is also fed via analog buffer 520 to an oscilloscope
display for viewing.
As shown in greater detail in FIGS. 6A, peak detector 540 includes
capacitor C1 with diode D1 to ensure that C1 charges up to the
highest (i.e., peak) input value when a transistor T1 is off. When
transistor T1 is on, it shorts C1 to ground and prevents it from
charging up. Transistor T1 is controlled by the Blanking
signal.
The output of peak detector 540 feeds sample and hold circuit 550.
The purpose of sample and hold circuit 550 is to hold the voltage
of capacitor C1 at the time period when the SAMPLE signal is
active. The end of the active period of the Sample signal
corresponds to the end of the time window described above. In this
manner, peak detector circuit 540 and sample and hold circuit 550
ensure that the peak of the Ultrasonic Input signal is measured
only during a certain time window corresponding to the local
thickness of the part under investigation.
The log amplifier and peak detector circuitry in FIGS. 6 and 6A
also includes an amplifier 560 to adjust the output of sample and
hold circuit 550 to the proper voltage range and current drive for
input to a microcomputer unit having an analog/digital converter
input (see FIG. 7). The purpose of the microcomputer, which could
instead be any type of appropriate analysis equipment depending
upon the system's requirements, is for acquiring and displaying
data for defect analysis. Of course, the microcomputer may also
perform whatever signal analysis is desired.
In accordance with the present invention, the apparatus for
ultrasonic inspection of a part also includes thickness gating
means for automatically adjusting the thickness value, and thereby
the time window, for the measuring means according to electrical
reflection signals received by the thickness transducer channel. In
the embodiment shown in FIGS. 2-7, the Three-position Gate in FIGS.
4 and 4A and the Thickness Gate Controller in FIGS. 5 and 5A adjust
a thickness value, which is called the Old Part Thickness Analog
value and is an analog voltage representation of the local part
thickness. The adjustment of that level involves the use of a
System Material Enable signal, which is a pulse whose duration
relates to the part thickness.
According to one variant of this invention, the thickness gating
means includes adjustable means for presetting the part thickness
value. A setup procedure is shown in FIG. 8, and will be explained
along with certain specific circuit elements of the Three-position
Gate and Thickness Gate Controller.
In the initialization step, the Ultrasonic Signal is adjusted by
placing switch 360 in the IF SYNC mode (step 605). As soon as the
signal strength is sufficient (steps 610 and 620), switch 360 is
changed to the GATE or thickness sync modes (Step 630).
Next, the IP sync adjustment potentiometer, which is VR-3 in FIG.
4A, is set so that the oscilloscope display of the GATE signal
(which, according to the switch setting, is the IP Sync Signal)
shows a high-to-low transition before the display reflection from
the front surface (step 640). The purpose of the IP sync signal is
to eliminate interference either from the Main Bang transmission
pulse, from reflector plates, or from any other source of
interference that would cause receipt of reflection prior to the
receipt of the front surface reflection.
Next, the IF blanking adjustment is set by aligning the transducer
with a thinner section of the part to be inspected and then using
the IF sync adjustment potentiometer VR4 in FIG. 4A to move a
low-to-high transition just after the display of the front surface
reflection (steps 650 and 660). Finally, the Initialize button is
pressed (step 670) which causes an initial thickness value to be
entered into old part thickness value D/A circuit 460, shown in
FIGS. 5 and 5A, in a manner to be described below. After this
procedure, the ultrasonic apparatus of this invention is now ready
for operation.
As shown in FIGS. 4 and 4A, the System Clock, which is a 15 MHz
clock generated in the Thickness Gate Controller, passes through a
TTL receiver 300 and a causes high speed counter 310 to begin
counting. Counter circuit 310 had previously been cleared by the
appropriate PULSER COMMAND. The output of counter circuit 310 then
feeds a digital/analog converter 320 which generates a ramp voltage
that tracks the count and has a level corresponding to the period
of time elapsed since the PULSER COMMAND.
The Old Part Thickness Analog Voltage signal, which, as indicated
above, is a voltage signal whose level represents the
currently-determined thickness of the part, is fed through a
thickness adjustment circuit 330. Circuit 330 allows an operator to
adjust the Old Part Thickness Analog Input to a comparator 340. The
ramp voltage and the adjusted Old Part Thickness Analog signal both
feed part thickness limiter comparator circuitry 340 shown in FIGS.
4 and 4A.
In the preferred embodiment and as shown in FIG. 4A, comparator 340
includes a monolithic chip comparator IC6 whose output changes
state when the ramp voltage exceeds the adjusted Old Part Thickness
Analog voltage. The system, and the thickness adjustment circuit
330, are set so that IC6's state change occurs just prior to the
anticipated receipt of a rear surface reflection, that anticipated
time being based on the believed thickness of the material as
reflected in the Old Part Thickness Analog signal.
The output of comparator 340 then feeds ultrasonic gate generator
370, assuming that switch 360 is properly set to the thickness sync
mode, to cause the generation of the GATE and SAMPLE signals. Both
signals have a predetermined duration determined by "one-shot" IC9.
The SAMPLE signal corresponds to the time window for measuring the
peak amplitude, since it is a pulse which last from a time just
prior to the anticipated receipt of a rear surface reflection, and
which remains high for a predetermined period of time sufficient to
allow capture of the entire anticipated rear surface reflection.
Each channel generates a GATE and SAMPLE signal.
In the preferred embodiment, the Three-Position Gate also generates
for each channel a Blanking signal used with the oscilloscope
display of the corresponding Ultrasonic Input signal. Only the
thickness transducer channel, however, generates a System Material
Enable signal and a Blanking signal for use in subsequent timing.
The Blanking signal for use in subsequent timing is shown in FIG.
4A as being generated by the flip-flop labelled IC7.
In accordance with the present invention, the thickness gating
means of this invention includes means for evaluating the
electrical reflection signals received by the thickness transducer
channel to determine a part thickness estimate. The System Material
Enable signal in the preferred embodiment of this invention may be
thought of as a part thickness estimate. That signal is generated
by signals received from interface timing generator 380 shown in
FIGS. 4 and 4A. Interface timing generator 380 includes IC8 which
is a monolithic chip comparator that compares the Ultrasonic Input
signal with a threshold value set using potentiometer VR-5. A high
output from IC8 means that the Ultrasonic Input signal has exceeded
the threshold. The first time that this occurs after the PULSER
COMMAND signal corresponds to the received reflection from the
front surface and causes the System Material Enable signal goes
from a low to a high level. The next time that IC8 generates a
pulse, which would correspond to receipt of reflections either from
the rear surface or from a defect, the System Material Enable
signal drops from a high to a low level. The "thickness estimate"
represented by the pulse duration of the System Material Enable
signal, will either represent a new thickness measurement or the
distance between the front surface and a defect. To determine which
value the System Material Enable signals represents, it is compared
to the current thickness value represented by the Old Part
Thickness Analog signal.
According to the present invention, there is means for replacing
the part thickness value with the part thickness estimate when the
part thickness value and estimate bear a predetermined relationship
with each offer. In the preferred embodiment, the testing of the
thickness part estimate and Old Part Thickness Analog signal is
performed by the Thickness Gate Controller shown in FIGS. 5 and 5A.
As seen in those figures, the System Material Enable signal causes
the counter enable 410 to gate the 15 MHz System Clock signals to
binary counter 420. The final count of counter 420 represents the
number of System Clock pulses which are gated through to the
counter during the System Material Enable signal. That final binary
count is the input to Part Thickness Estimate D/A circuit 440,
whose analog voltage output reflects that final count.
A digital value corresponding to the Old Part Thickness Analog
signal has previously been stored in a register internal to the old
part thickness value D/A circuit 460. That value was initially
input when the Initialize button 430 was pushed, which activated
the load input to circuit 460 and caused it to store the binary
count generated during the initialization. Thereafter, the digital
value in the old part thickness value D/A circuit 460 is
periodically updated as described below.
The output of the old part thickness value D/A circuit 460
represents the Old Part Thickness Analog level, which is also made
available to the Three-position Gate via Analog Voltage Buffer 480.
The Old Part Thickness Analog signal and the part thickness
estimate are input to the part thickness comparator circuitry 470
which is shown in greater detail in FIG. 5A. In the embodiment
shown in FIG. 5A, the part thickness estimate is fed through
amplifiers A1 and A2, which multiply the part thickness estimate by
values greater and less than unity, respectively. Preferably those
values are 1.05 and 0.95, which represent a .+-.5% deviation, but
the potentiometers in the feedback circuit for amplifiers A1 and A2
may be adjusted for different values. These multiple values are
inputs to part thickness comparator circuitry 470 along with the
Old Part Thickness Analog signal. If the part thickness estimate is
greater than 0.95 and less than 1.05 the Old Part Thickness Analog
level (or within other limits if the .+-.5% deviation are not
used), then the output of part thickness comparator circuitry 470
changes state and cause new part thickness "valid" pulse generator
450 to load the digital output of counter 420, which corresponds to
the part thickness estimate, into old part thickness value D/A
circuit 460. This causes an updating of the Old Part Thickness
Analog value. If, however, the part thickness estimate is outside
of the predetermined range, then the Old Part Thickness Value
stored in circuit 460 remains the same.
FIG. 9 shows the timing relationship of the signals just discussed.
FIG. 9A is the System Clock, FIG. 9B is the Ultrasonic Input
Signal, FIG. 9C is the PULSER COMMAND, FIG. 9D is the output of D/A
converter 320, FIG. 9F is the Old Part Thickness Analog signal, and
FIG. 9F is the output of the comparator 340, which switches state
when the signals 9D and 9E (as adjusted) are equal, i.e. at voltage
V.sub.t. As described above, this equality causes the generation of
the GATE (and SAMPLE) signal as shown in FIG. 9G. FIG. 9H is the
System Material Enable signal.
It will be apparent to those skilled in the art that modifications
and variations can be made in the ultrasonic inspection apparatus
and methods of this invention. The invention in its broader aspects
is not limited to the specific details, representative methods and
apparatus, and illustrative examples shown and described. Departure
may be made from such details without departing from the spirit or
scope of the general inventive concept.
* * * * *